1. FIELD OF THE INVENTION
This invention relates to a method of producing the partially hydrolyzed acrylamide polymers, and more particularly it relates to a method of producing the partially hydrolyzed solid-state acrylamide polymers in an industrially advantageous way from a highly viscous hydrous acrylamide polymer gel obtained by polymerization in an aqueous medium. The term "acrylamide polymers" used in this specification is to be understood as signifying both homopolymers of acrylamide and copolymers containing acrylamide.
2. DESCRIPTION OF PRIOR ART
The partially hydrolyzed acrylamide polymers are generally used as flocculant, paper strengthening agent and for various other purposes. The partially hydrolyzed acrylamide polymers are produced usually by treating an acrylamide polymer with an alkaline material such as for example caustic soda to hydrolyze the amide groups. Acrylamide polymers are usually produced by polymerizing the monomer in a 10 to 35 wt% aqueous solution, but as the acrylamide polymers thus obtained are in the form of a hard hydrous rubber-like gel, no uniform contact of such gel with an alkaline material is obtained when mixing them by a common method, and hence it is hardly possible with such method to accomplish uniform hydrolysis of a desired degree. As a means for hydrolyzing such hydrous polymer gel, there has been proposed a method of kneading the gel and an alkaline material by using a rotary screw extruder (Japanese Patent Publication No. 17668/1974). This method is capable of accomplishing hydrolysis steadily and uniformly, with no risk of causing local hydrolysis, but it has a serious drawback that there could occur shear degradation of molecular weight or quality deterioration of the polymer owing to the strong shearing force that develops in the presence of an alkaline material, resulting in the reduced commercial value of the products.
The present inventors have applied themselves to the study aimed at overcoming such problems and found out that it is possible to accomplish hydrolysis of a desired degree, without causing any deterioration of the polymer quality or local hydrolysis, if the gel used for the hydrolysis is previously pulverized into particles and then mixed with an alkaline material by using a specific apparatus, and that the hydrolysis can be advanced favorably by subjecting the mixture to drying under heating immediately following the above-said operation. This invention was attained on the basis of such findings.